Control system, controller, and control method for wound induction machine

Abstract

According to one embodiment, a control system includes a chopper, a short-circuit unit, a voltage detector circuit, and a controller. The chopper reduces a direct current voltage between a converter connected to a stator in a wound induction machine and an inverter connected to a rotor in the wound induction machine. The short-circuit unit shorts a wire used for connection between the rotor and the inverter and the voltage detector circuit is to detect the direct current voltage. The controller causes driving the chopper and, at the same time, outputting from the inverter an alternating current over which a direct current component is superimposed when a voltage value exceeds a first predetermined value, and causes driving the short-circuit unit and, at the same time, halting the inverter when the voltage value exceeds a second predetermined value.

The invention claimed is: 
     
       1. A control system of a wound induction machine, comprising:
 a chopper to reduce a direct current voltage between a converter connected to a stator in the wound induction machine and an inverter connected to a rotor in the wound induction machine; 
 a short-circuit unit to short a wire used for connection between the rotor and the inverter; 
 a voltage detector circuit to detect the direct current voltage; and 
 a controller to cause driving the chopper and, at the same time, outputting from the inverter an alternating current superimposed over a direct current component when a voltage value input from the voltage detector circuit exceeds a first predetermined value, and to cause driving the short-circuit unit and, at the same time, halting the inverter when the voltage value exceeds a second predetermined value higher than the first predetermined value. 
 
     
     
       2. The control system according to  claim 1 , further comprising a current sensor to detect line current flowing through the wire, wherein
 when one circuit breaker is connected between the stator and an electric power system, the controller causes the wound induction machine to halt after the current value of the line current falls below a predetermined current value, and 
 when any one of the multiple circuit breakers is connected between the stator and the electric power system, the controller causes the wound induction machine to continue operating after the current value falls below the predetermined current value. 
 
     
     
       3. The control system according to  claim 2 , wherein the controller temporarily increases the predetermined current value from the time at which both the chopper and the inverter are driven in accordance with the first predetermined value to the time at which the short-circuit unit is driven in accordance with the second predetermined value. 
     
     
       4. The control system according to  claim 1 , wherein the short-circuit unit includes a short-circuit switching element across the wire, and a current limit resistor series-connected to the short-circuit switching element. 
     
     
       5. The control system according to  claim 1 , wherein
 the chopper includes a chopper switching element and a chopper resistor series-connected to the chopper switching element, and 
 the resistance of the chopper resistor is set to a value at which the voltage value does not exceed the second predetermined value. 
 
     
     
       6. A control method for a wound induction machine including a stator connected to an electric power system through at least one circuit breaker, and a rotor provided in the stator, the control method comprising:
 detecting a direct current voltage between a converter connected to the stator and an inverter connected to the rotor; 
 driving a chopper to reduce the direct current voltage and, at the same time, outputting from the inverter an alternating current over which a direct current component is superimposed when the detected voltage value exceeds a first predetermined value; and 
 shorting a wire used for connection between the rotor and the inverter and, at the same time, halting the inverter when the voltage value exceeds a second predetermined value higher than the first predetermined value. 
 
     
     
       7. A controller for a wound induction machine including a stator connected to an electric power system through at least one circuit breaker, and a rotor provided in the stator, the controller comprising:
 a determination unit to determine whether a voltage value corresponding to a direct current voltage between a converter connected to the stator and an inverter connected to the rotor exceeds a first predetermined value, and whether the voltage value exceeds a second predetermined value higher than the first predetermined value; and 
 a command unit to cause driving a chopper which reduces the direct current voltage and, at the same time, outputting from the inverter an alternating current over which a direct current component is superimposed when the determination unit determines that the voltage value exceeds the first predetermined value, and to cause driving a short-circuit unit which shorts a wire used for connection between the rotor and the inverter and, at the same time, halting the inverter when the determination unit determines that the voltage value exceeds the second predetermined value.